Light emitting device and plant cultivation method

Abstract

A light emitting device includes a light emitting element having an emission peak wavelength in a range of 380 nm or more and 490 nm or less, and a red fluorescent material which is excited by the light from the light emitting element to emit light having at least one light emission peak wavelength in a range of 580 nm or more and 680 nm or less, wherein a ratio of the photon flux R of red light in a range of 620 nm or more and 700 nm or less to the photon flux B of blue light in a range of 400 nm or more and 490 nm or less, R/B, is in a range of more than 20 and 200 or less.

The invention claimed is: 
     
       1. A light emitting device comprising:
 a light emitting element having an emission peak wavelength in a range of 380 nm or more and 490 nm or less; and 
 a red fluorescent material which is excited by the light from the light emitting element to emit light having at least one light emission peak wavelength in a range of 580 nm or more and 680 nm or less, wherein 
 a ratio of a photon flux R of red light in a range of 620 nm or more and 700 nm or less to a photon flux B of blue light in a range of 400 nm or more and 490 nm or less, R/B, is in a range of more than 20 and 200 or less. 
 
     
     
       2. The light emitting device according to  claim 1 , wherein the ratio R/B is in a range of 50 or more and 120 or less. 
     
     
       3. The light emitting device according to  claim 1 , wherein a light emission spectrum of the light emitting device has at least one light emission peak in a range of 580 nm or more and 680 nm or less and the full width at half maximum of the emission peak is 40 nm or more. 
     
     
       4. The light emitting device according to  claim 1 , wherein the red fluorescent material comprises an Eu 2+ -activated silicon nitride comprising Al and at least one element selected from Sr and Ca. 
     
     
       5. The light emitting device according to  claim 1 , wherein the red fluorescent material comprises at least one selected from the group consisting of:
 an Eu 2+ -activated aluminum nitride comprising at least one element selected from the group consisting of an alkaline earth metal element and at least one element selected from the group consisting of an alkali metal element, 
 an Mn 4+ -activated fluorogermanate fluorescent material, 
 an Eu 2+ -activated, Ca or Sr sulfide, and 
 an Mn 4+ -activated fluoride comprising at least one element or ion selected from the group consisting of an alkali metal element and an ammonium ion (NH 4 +) and at least one element selected from the group consisting of a Group-4 element and a Group-14 element in the composition thereof. 
 
     
     
       6. The light emitting device according to  claim 1 , wherein the red fluorescent material comprises a composition represented by the following formula (I):
   (Ca 1-s-t Sr s Eu t ) x Al u Si v N w    (I)
 
 
       wherein s, t, u, v, w and x each satisfy 0≤s≤1, 0<t<1.0, 0<s+t<1.0, 0.8≤x≤1.0, 0.8≤u≤1.2, 0.8≤v≤1.2, 1.9≤u+v≤2.1, and 2.5≤w≤3.5. 
     
     
       7. The light emitting device according to  claim 1 , which is used in combination with a white light emitting light source. 
     
     
       8. The light emitting device according to  claim 1 , which is used for plant cultivation. 
     
     
       9. An illumination device comprising a combination of the light emitting device of  claim 1 , and a light source that emits a light energy different from that of the light emitting device of  claim 1 . 
     
     
       10. A plant cultivation method comprising irradiating plants with the light emitted by the light emitting device of  claim 1 .